The commission's 10-0 vote followed a marathon hearing in the Santa Monica Civic Auditorium. Commission staff and environmentalists debated utility officials throughout the day over the potential damage the sonic blasts would cause near scenic Morro Bay on the Cental California coast.

The tests would have potentially deadly effects on threatened and endangered marine mammals, including whales, sea otters and 2,000 harbor porpoises that could be driven out of their Morro Bay foraging grounds, staff members said.